Patent application title: AIRBAG COVER AND AIRBAG APPARATUS

Abstract:

An airbag cover and an airbag apparatus are provided which achieve cost
reduction by integrally molding an instrument panel and an inner case as
well as ensure the rigidity of the instrument panel without degrading the
aesthetically pleasing of the instrument panel. An airbag cover according
to one form of the present invention is an airbag cover that is formed by
integrally molding a plate-like portion constituting a vehicle interior
surface and an inner case that is disposed on the back face of the
plate-like portion and constitutes an airbag inflation and deployment
path, wherein the plate-like portion constitutes part of the instrument
panel disposed in front of an occupant, and the inner case is formed in a
position in front of an occupant in a passenger seat, and the side close
to a driver's seat of the plate-like portion is formed so as to be
disposed in the back of a convex portion formed in the middle of the
instrument panel, into which onboard equipment is set.

Claims:

1. An airbag cover comprising:a plate portion for extending over an
airbag;depending leg portions extending transverse to the plate portion
and formed integrally therewith so that the plate portion and leg
portions are of a single piece construction;a tear line of the plate
portion generally between the leg portions;an opening formed in the plate
portion upon airbag deployment and rupture of the tear line;
andperipheral portions of the plate portion extending beyond the leg
portions and being sized so that the plate portion has a surface area
that is several times greater than of the opening formed in the plate
portion.

2. The airbag cover of claim 1, wherein the plate portion surface area is
approximately 1000 cm2 to approximately 2000 cm2 and is
approximately three to eight times that of the opening in the plate
portion.

3. The airbag cover of claim 1 wherein the peripheral portions including
an outermost rim edge, and the opening is disposed at least 30 mm away
from the rim edge of the plate portion.

4. The airbag over of claim 1 wherein the plate portion and the leg
portions are of an olefin thermoplastic resin which has the following
characteristics:(a) bending modulus of elasticity (JIS-K7203): 500 to
1000 MPa,(b) tensile break strength: 15 to 40 MPa,(c) stretch at break:
600% or more, and(d) Izod impact strength: not to break away at -35
degrees centigrade or more.

5. The airbag cover of claim 1, wherein the plate portion has a thickness
of 2.5 mm to 3.5 mm, and at least one of the leg portions is partially
thicker than the plate portion.

6. The airbag cover of claim 1, wherein the plate portion includes a door
that splits open along the tear line upon airbag deployment, anda hinge
portion between the plate portion and at least one of the leg portions
that rotatably holds the door and which has a thin portion thinner than
the one leg portion.

7. The airbag cover according to claim 6, wherein the hinge portion has a
plurality of ribs disposed on an external surface of the thin portion so
as to be bendable and bucklable upon airbag deployment and door rotation.

8. The airbag cover of claim 1 in combination with an instrument panel
have an opening for the mounting of the vehicle instruments therein, and
wherein the airbag cover is sized to have an outer peripheral edge
thereof mounted adjacent to the opening of the instrument panel to
integrate the instrument panel with the airbag cover.

9. An instrument panel assembly for a vehicle, the instrument panel
assembly comprising:an instrument panel having a convex portion and an
opening for vehicle instrumentation with the convex portion extending
along the opening;an airbag cover generally aligned with the instrument
panel and including a frangible plate portion;leg portions integrally
formed with the plate portion to depend therefrom with the leg portions
operable to guide a deploying airbag upwardly therealong to rupture the
frangible plate portion; andan outer side portion of the frangible plate
portion that extends adjacent to and along the convex portion of the
instrument panel to form an interface between the instrument panel and
the airbag cover that is minimally visible or hidden to an occupant of
the vehicle.

10. The instrument panel assembly of claim 9 wherein the instrument panel
convex portion has a backside adjacent a windshield of the vehicle, and
the outer side portion of the airbag cover plate portion extends along
the backside of the instrument panel convex portion.

11. The instrument panel assembly of claim 9 wherein the instrument panel
convex portion and the outer side portion of the airbag cover plate
portion have matching configurations at the interface therebetween.

12. The instrument panel assembly of claim 9 wherein the frangible plate
portion has a door that splits open upon airbag deployment to form an
opening in the frangible plate portion for the deploying airbag, and the
plate portion including the outer side portion thereof is sized to have a
surface area that is several times larger than that of the opening.

13. The instrumental panel assembly of claim 12, wherein the door is
formed by a tear line in the plate portion so as to split open, and the
tear line is formed by any one of machining, laser beam machining, and
ultrasonic machining which follows forming of the airbag cover.

14. The instrument panel assembly of the claim 12 wherein the surface area
of the plate portion is between approximately 1000 cm2 and
approximately 2000 cm2 and the surface area of the opening is
between approximately 250 cm2 and approximately 300 cm.sup.2.

15. The instrument panel assembly of claim 9 wherein the plate portion and
the leg portions are of an olefin thermoplastic resin which has the
following characteristics:(a) bending modulus of elasticity (JIS-K7203):
500 to 1000 MPa,(b) tensile break strength: 15 to 40 MPa,(c) stretch at
break: 600% or more, and(d) Izod impact strength: not to break away at
-35 degrees centigrade or more.

16. The instrument panel assembly of claim 9 in combination with the
vehicle having a front driver's seat and a front passenger's seat, and
wherein the leg portions are in front of the passenger's seat, and plate
portion is sized so that the outer side portion extends to be closer to
the driver's seat than the passenger's seat.

Description:

FIELD OF THE INVENTION

[0001]The present invention relates to an airbag cover constituting a
fracture-opening section and an airbag apparatus provided with such an
airbag cover, and more specifically, it relates to an airbag cover
suitable for an airbag and an airbag apparatus that are disposed in an
instrument panel constituting a vehicle interior surface panel.

BACKGROUND OF THE INVENTION

[0002]A vehicle such as an automobile is generally provided with an airbag
apparatus that deploys in a passenger compartment to restrain occupants
in the event of an emergency such as a crash. Various types of airbag
apparatuses have been developed and adopted as such an airbag, including
a driver's airbag apparatus mounted inside a steering wheel, a passenger
airbag apparatus mounted in an instrument panel, a side airbag apparatus
mounted in a vehicle side door or an outboard side of a seat, and a knee
airbag apparatus mounted under a dashboard. These airbag apparatuses are
mounted inside a vehicle structure so as to be normally hidden, and are
designed to split open part of the vehicle structure and inflate and
deploy an airbag in a passenger compartment in the event of an emergency
such as a crash. Accordingly, a fracture-opening section for an airbag
must be normally covered so as to be merged with a vehicle interior
surface panel, while it must split open so that an airbag smoothly and
rapidly inflates and deploys in the event of an emergency.

[0003]The afore mentioned airbag apparatus includes an airbag that is
normally stored in a folded state and inflates and deploys in case of an
emergency, an inflator for supplying gas to the airbag, a retainer for
housing the airbag, and an airbag cover that locks the retainer thereto
and constitutes a vehicle interior surface panel. The airbag cover is a
resin-molded, thin plate-like body and has a groove called a tear line
formed on its back face. A door to be defined when the airbag cover
splits open is rotatably supported by a hinge portion formed in the
airbag cover and constitutes a fracture-opening section for inflating and
deploying an airbag.

[0004]Various types of passenger airbag apparatuses to be mounted on an
instrument panel have been developed as disclosed in Japanese Unexamined
Patent Application Publication No. 2-171364 and Japanese Unexamined
Patent Application Publication No. 2003-137057. The airbag apparatus
disclosed in Japanese Unexamined Patent Application Publication No.
2-171364 has an airbag cover that is formed so as to be slightly larger
than an opening. During the early years of introduction of airbags, an
airbag cover was often disposed only at a place necessary for the
inflation and deployment of an airbag and was set into an instrument
panel, as described in Japanese Unexamined Patent Application Publication
No. 2-171364. However, such an airbag cover posed a problem in that it
was not aesthetically pleasing because of its exposure to the front of an
occupant and also it limited the flexibility of design.

[0005]As described in Japanese Unexamined Patent Application Publication
No. 2003-137057, disposing an inner case having an airbag module on the
back face of an instrument panel has recently become mainstream. In the
case of an airbag apparatus of such a type, the instrument panel must be
formed of a hard resin because of the necessity of rigidity so that it
does not break away at the time of the inflation and deployment of an
airbag. To attain this purpose, an inner case made of a soft resin is
connected by welding to the back face of the instrument panel so that a
door constituting an airbag fracture-opening section turns instead of
breaking away.

[0006]However, in the case of an airbag apparatus described in Japanese
Unexamined Patent Application Publication No. 2003-137057, an instrument
panel and an inner case are separately constructed, which causes an
increase in the number of parts and processes required for connecting
them, resulting in an increase in the cost of an airbag apparatus.

SUMMARY OF THE INVENTION

[0007]The present invention has been achieved to solve the above-mentioned
problems. Accordingly, an object of the present invention is to provide
an airbag cover and an airbag apparatus that achieve cost reduction by
forming an instrument panel and an inner case in an integral manner as
well as maintaining the rigidity of the instrument panel without
degrading an aesthetically pleasing appearance.

[0008]According to the present invention, an airbag cover is formed by
integrally molding a plate-like portion constituting a vehicle interior
surface and an inner case that is disposed on the back face of the
plate-like portion and constitutes an airbag inflation and deployment
path, wherein the plate-like portion constitutes part of the instrument
panel disposed in front of an occupant, and the inner case is formed in a
position in front of an occupant in a passenger seat, and the side close
to a driver's seat of the plate-like portion is formed so as to be
disposed in the back of a convex portion formed in the middle of the
instrument panel, into which onboard equipment is set, and the plate-like
portion and the inner case are made of an olefin thermoplastic resin
which meets: (A) bending modulus of elasticity (JIS-K7203): 500 to 1000
MPa, (B) tensile break strength: 15 to 40 MPa, (C) stretch at break: 600%
or more, (D) Izod impact strength: not to break away at -35 degrees
centigrade or more.

[0009]According to the present invention, an airbag apparatus includes an
airbag that is normally folded and inflates and deploys in case of an
emergency, an inflator for supplying a gas to the airbag, a retainer that
houses at least the airbag and has a hook on an outer surface thereof,
and an airbag cover that locks the retainer thereto and constitutes a
vehicle interior surface, wherein the airbag cover is formed by
integrally molding a plate-like portion constituting part of an
instrument panel disposed in front of an occupant and an inner case
disposed on the back face of the plate-like portion, which constitutes an
airbag inflation and deployment path and has a locking hole at its leg
portion to which the hook is locked, wherein the plate-like portion
constitutes part of the instrument panel disposed in front of an
occupant, and the inner case is formed in a position in front of an
occupant in a passenger seat, and the side close to a driver's seat of
the plate-like portion is formed so as to be disposed in the back of a
convex portion formed in the middle of the instrument panel, into which
onboard equipment is set, and wherein the plate-like portion and the
inner case are made of an olefin thermoplastic resin which meets: (A)
bending modulus of elasticity (JIS-K7203): 500 to 1000 MPa, (B) tensile
break strength: 15 to 40 MPa, (C) stretch at break: 600% or more, (D)
Izod impact strength: not to break away at -35 degrees centigrade or
more.

[0010]In the airbag cover and the airbag apparatus, the plate-like portion
may have a surface area of 1000 to 2000 cm2 and may have a size
approximately three to eight times that of an opening of the airbag, and
the opening may be disposed at least 30 mm away from the outer
circumferential edge of the plate-like portion.

[0011]Also, in the airbag cover and the airbag apparatus, the plate-like
portion may have a thickness of 2.5 mm to 3.5 mm, and the leg portion of
the inner case may be partially thicker than the plate-like portion.

[0012]In addition, in the airbag cover and the airbag apparatus, the
plate-like portion may include a door that is formed so as to split open
when the airbag inflates and deploys and a hinge portion that rotatably
holds the door, and a connecting section with the inner case of the hinge
portion may have a thinner portion having a thickness of 0.5 mm to 1.5
mm. The hinge portion may have a plurality of ribs disposed on the
external surface of the thinner portion so as to be bendable and
bucklable when the airbag inflates and deploys.

[0013]Furthermore, the door is formed by a tear line formed in the
plate-like portion so as to split open, and the tear line may be formed
by machining, laser beam machining, or ultrasonic machining which follows
forming of the airbag cover.

[0014]The airbag cover and the airbag apparatus according to the present
invention solves the problems that have been encountered with a
conventional airbag apparatus by providing a medium-size airbag cover
because an airbag apparatus of an early date poses an aesthetic problem
due to its too small airbag cover while a recent airbag apparatus poses a
problem in that its too large airbag cover like the entire instrument
panel makes it difficult to keep the rigidity and to prevent the door
from breaking away.

[0015]The airbag cover and the airbag apparatus according to the present
invention can attain a reduction in the number of parts and a reduction
of man-hours by integrally molding a plate-like portion and an inner
case. In addition, the use of an olefin thermoplastic resin meeting a
predetermined requirement in the airbag cover as well as a medium-size
plate-like portion constituting part of an instrument panel improves in
rigidity of the instrument panel despite the use of the soft resin.
Furthermore, disposition of the side of the plate-like portion in the
back of a convex portion in the instrument panel allows a seam between
the airbag cover and the instrument panel to be disposed so as to be
hardly visible to or hidden from occupants in the driver's seat and the
passenger seat, thereby keeping the instrument panel aesthetically
pleasing.

[0016]Also, limitation of the surface area of the plate-like portion to a
predetermined size to determine the location of the opening leads to
improvement in rigidity of the instrument panel. The plate-like portion
having smaller wall thickness ant the inner case leg portion having
larger wall thickness allow the plate-like portion to more easily split
open and turn at the time of airbag inflation and deployment as well as
enhance the rigidity of the inner case leg portion to which the retainer
is locked.

[0017]A thinner portion formed in a connecting section between the
plate-like portion and the inner case suppresses deformation of the
connecting section resulting from contraction associated with curing of a
resin, which prevents sink from occurring on the surface of the airbag
cover, resulting in improvement in the appearance of the airbag cover. In
addition, a plurality of ribs disposed on the outer surface of such a
thinner portion of the hinge eliminates the necessity for a thinner
portion constituting a hinge to be separately formed in the plate-like
portion, resulting in a simplified hinge structure. Furthermore, the ribs
formed so as to be bendable and bucklable can absorb an impact created at
the time of turning of the door, thereby effectively preventing the door
from breaking away.

[0018]Forming the tear line by any one of machining, laser beam machining,
and ultrasonic machining which follows the forming of the airbag cover
simplifies the mold of the airbag cover, which reduces the cost for
designing and manufacturing the mold, leading to reduction in cost of an
airbag apparatus.

[0022]FIG. 4 shows the relationship between material for use in airbag
cover and the surface area.

[0023]FIGS. 5(A)-5(C) are views showing an airbag cover according to the
present invention. FIG. 5(A) is a cross-sectional view. FIG. 5(B) is an
enlarged view of a section indicated by "B" in FIG. 5(A). FIG. 5(C) is an
enlarged view of a section indicated by "C" in FIG. 5(A).

[0024]FIGS. 6(A) and 6(B) are views showing an airbag cover according to
the present invention. FIG. 6(A) is a rear view. FIG. 6(B) is a
cross-sectional view taken along the line B-B of FIG. 6(A).

[0025]FIGS. 7(A) and 7(B) are schematic illustrations showing part of
manufacturing process of an airbag cover according to the present
invention. FIG. 7(A) shows a molding process of a thinner portion. FIG.
7(B) shows a working process of a tear line.

[0026]FIGS. 8(A) and 8(B) are illustrations showing how an airbag inflates
and deploys. FIG. 8(A) shows an airbag just before released to the
passenger compartment. FIG. 8(B) shows an airbag immediately after
released to the passenger compartment.

[0027]FIG. 9 is a cross-sectional view of an airbag according to the
present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028]An embodiment of the present invention will be described below with
reference to FIGS. 1(A) to 9. FIGS. 1(A)-1(C) are external views showing
an airbag cover according to the present invention and a conventional
airbag cover. FIG. 1(A) shows an airbag cover according to the present
invention. FIG. 1(B) shows a small, conventional airbag cover. FIG. 1(C)
shows a large, conventional airbag cover.

[0029]As shown in FIG. 1(A), an airbag cover according to the present
invention is formed by integrally molding a plate-like 11 portion
constituting a vehicle interior surface and an inner case 12 that is
disposed on the back face of the plate-like portion and constitutes an
airbag inflation and deployment path. The plate-like portion 11
constitutes part of the instrument panel 2 disposed in front of an
occupant, and the inner case 12 is formed in a position in front of an
occupant in a passenger seat P, and the side 13 close to a driver's seat
D of the plate-like portion 11 is formed so as to be disposed in the back
of a convex portion 21 formed in the middle of the instrument panel 2,
into which onboard equipment is set. Views of the driver's seat and the
passenger seat show only a seating surface and omit an illustration of a
seat back.

[0030]The convex portion 21 corresponds to a section called a meter hood
or a center instrument panel, and is formed on the instrument panel in
the shape of a substantial half-moon or a rectangle. An opening 22 formed
inside the convex portion 21 constitutes a space into which a
speedometer, a tachometer, a fuel gauge, an air conditioner louver, a
control panel, a car audio system, a car navigation system, and a hazard
switch are incorporated. The side 13 of the plate-like portion 11 is
shaped so as to fit the shape of the back (close to the windshield) of
the convex portion 21. For example, as shown in FIG. 1(A), if the back of
the convex portion 21 is formed in a curved shape, the side 13 is curved
so as to fit the curved shape. Needless to say, if the back of the convex
portion 21 is formed in a linear or rectangular shape, the side 13 is
formed to fit the linear or rectangular shape. The other side 14 of the
plate-like portion 11 is formed to fit the shape of the windshield close
to the instrument panel 102. The use of the airbag cover 1 employing the
plate-like portion 11 of such a shape allows a seam between the airbag
cover 1 and the instrument panel 2 to be disposed so as to be hardly
visible to or completely hidden from occupants in a driver's seat and a
passenger seat, thereby keeping an aesthetically pleasing appearance. In
particular, in order to make the seam less visible to the occupant in the
passenger seat P, the end of the side 13 of the plate-like portion is
disposed in the back of the convex portion 21 so as to be closer to the
driver's seat D (to the side of the driver's seat D of the center line of
the instrument panel 102). Although FIG. 1(A) shows that the side 13 of
the plate-like portion 11 is shaped so as to be disposed close to the
driver's seat D along the back face of the convex portion 21, such a
shape is not limited to this. Any disposition of the seam between the
airbag cover 1 and the instrument panel 2 in a position completely hidden
from or hardly visible to the occupants using the convex portion 21 poses
no problem. For example, the side 13 of the plate-like portion 11 may be
shaped in such a manner that the side 13 of the plate-like portion 11
constitutes part of the back face of the convex portion 21, or be shaped
to be disposed in the back face without fitting the shape of the convex
portion 21, or be shaped so as to be disposed close to the passenger seat
P.

[0031]An airbag cover according to the present invention is compared to a
conventional airbag cover in terms of structure. As shown in FIG. 1(B), a
conventional, small airbag cover 101 is disposed in an instrument panel
102 so as to be located in front of a passenger seat. Also, the airbag
cover 101 has an inner case 103 formed in an integral manner on an inner
surface thereof. In the conventional, small airbag cover 101, a seam
between the airbag cover 101 and the instrument panel 103 is exposed to
the front face, which degrades its appearance.

[0032]A large, conventional airbag cover 104 as shown in FIG. 1(C)
constitutes an instrument panel itself ranging from the passenger seat to
the driver's seat, and has an inner case 105 as a separate component
connected by welding to an inner surface thereof Due to being the
instrument panel itself the large airbag cover 104 has no seam and
therefore provides an aesthetically feasible appearance. In contrast, due
to its large size the airbag cover 104 has a problem of low rigidity and
a door that breaks away. To solve these problems, an inner case 105 is
separately constructed and mounted on the airbag cover 104 (instrument
panel). However, the instrument panel (airbag cover 104) and the inner
case 105 being separately constructed results in an increase in the
number of parts and manufacturing processes, leading to increased cost of
an airbag apparatus.

[0033]The present invention attains a reduction in the number of parts and
a reduction of man-hours by integrally molding the plate-like portion 11
and the inner case 12. In addition, the rigidity of the instrument panel
2 is improved by using an olefin thermoplastic resin meeting a
predetermined requirement in the airbag cover 1 and forming a plate-like
portion 11 into a medium-size constituting part of an instrument panel 2.
Furthermore, a seam between the airbag cover and the instrument panel is
disposed so as to be hardly visible to or hidden from occupants in the
driver's seat D and the passenger seat P by disposing the side 13 of the
plate-like portion 11 in the back of a convex portion 21 in the
instrument panel 2, thereby keeping the instrument panel aesthetically
pleasing.

[0034]FIG. 2 is a diagram showing a target of an airbag cover according to
the present invention. In this figure, the horizontal axis depicts a
surface area (cm2) of an airbag cover, while the vertical axis
depicts the bending modulus of elasticity (MPa).

[0035]Curves L1, L2 indicated by dashed-dotted lines in FIG. 2 depict a
relationship between a surface area and bending modulus of elasticity of
conventional airbag covers 101, 104. The curve L1 represents a small
airbag cover 101 as shown in FIG. 1(B), where its surface area is less
than 1000 cm2 and bending modulus of elasticity is up to approximately
500 MPa. The airbag cover 101 represented by the curve L1, is small, and
therefore can maintain its rigidity even if it is made of a soft resin
like an olefin thermoplastic resin (TPO material). In contrast, the curve
L2 represents a large airbag cover 104 as shown in FIG. 1(C), where its
surface area is more than 2000 cm2 and bending modulus of elasticity is
up to approximately 1500 MPa. Due to its large size, the airbag cover 104
represented by the curve L1 cannot use a soft resin like TPO material,
but use a hard resin like polypropylene resin (PP material). There is a
medium-size airbag cover having a surface area of 1000 to 2000 cm2, which
constitutes the entire instrument panel. Like the large airbag cover 104,
the medium-size airbag cover uses a hard resin to keep its rigidity since
a soft resin does not provide such rigidity.

[0036]The airbag cover 1 according to the present invention is targeted at
an airbag cover which falls within the shaded region T in FIG. 2. In
other words, the airbag cover according to the present invention is a
medium-size airbag cover having surface area of 1000 to 2000 cm2 with
bending modulus of elasticity of 500 to 1000 MPa. In addition, the airbag
cover according to the present invention uses an olefin thermoplastic
resin (TPO), a soft resin, because it is formed by integrally molding the
plate-like portion 11 and the inner case 12. Use of the olefin
thermoplastic resin (TPO) allows bending modulus of elasticity to be
increased to up to 1000 MPa by blending its components such as
polypropylene resin, ethylene propylene copolymer rubber, and ethylene
octane copolymer rubber in an appropriate manner.

[0037]As described above, the airbag cover according to the present
invention uses an olefin thermoplastic resin (TPO) that is a soft resin.
Property evaluation as to bending modulus of elasticity only is
insufficient for product commercialization. FIG. 3 shows the results of a
property evaluation and product evaluation carried on specimens prepared
with an olefin thermoplastic resin (TPO material). In this figure, a
hyphen ("-") indicates no data obtained for an appropriate item.

[0038]Specimens 1 to 3 have components such as polypropylene resin,
ethylene propylene copolymer rubber, and ethylene octane copolymer rubber
blended in such a manner that their bending modulus of elasticity
pursuant to JIS-K7203 falls within 500 to 1000 MPa, as shown in the
property evaluation column. More specifically, specimen 1 had bending
modulus of elasticity of 500 MPa, specimen 2 had bending modulus of
elasticity of 620 MPa, and specimen 3 had bending modulus of elasticity
of 760 MPa. Then, a property evaluation was carried out on each of
specimens 1 to 3 in terms of tensile break strength, stretch at break,
and Izod impact strength.

[0039]For tensile break strength and stretch at break, tensile tests were
performed on a JIS-K6251 dumbbell specimen No. 5 at a speed of 50 mm/min.
These tests show that specimen 1 has tensile break strength of 8.6 MPa,
specimen 2 has tensile break strength of 15.1 MPa, and specimen 3 has
tensile break strength of 9.3 MPa. Also, specimen 1 has stretch at break
of 100%, specimen 2 has stretch at break of 600%, and specimen 3 has
stretch at break of 200%.

[0040]For Izod strength, Izod impact strength tests were performed on
specimens having a notch formed therein at -20, -35, -40, and -45 degrees
centigrade. These tests show that specimen 3 breaks away when subjected
to impact energy of 16.5 kj/m2 at -20 degrees centigrade, breaks
away when subjected to impact energy of 10.7 kj/m2 at -35 degrees
centigrade, and breaks away when subjected to impact energy of 9.1
kj/m2 at -40 degrees centigrade. Generally, any component to be
mounted on a vehicle must withstand temperatures ranging from -35 (low
temperature) to 85 degrees centigrade (high temperature). From this point
of view, specimen 3 already breaks away at temperatures of -20 to -40
degrees centigrade, and did not receive the test at -45 degrees
centigrade since the test at -45 degrees centigrade is judged to be not
necessary. Also, specimen 2 does not break (N.B.) away at -20, -35, and
-40 degrees centigrade, and breaks away when subjected to impact energy
of 13.3 kj/m2 at -45 degrees centigrade. In addition, specimen 1
breaks away when subjected to impact energy of 6.1 kj/m2 at -45
degrees centigrade, and breaks away when subjected to impact energy of
9.3 kj/m2 at -40 degrees centigrade. The test results of specimen 1
at -40 and -45 degrees centigrade clearly show that breakage occurs even
at more than -35 degrees centigrade. Accordingly, tests at -20 and -35
degrees centigrade were not performed.

[0041]Furthermore, product evaluations were performed on specimens 1 to 3.
In these product evaluations, a medium-size airbag cover having a
surface area of 1302 cm2 (integral inner case) was prepared, and
thickness of the plate-like portion and the thickness of the hinge
portion were set at 3 mm and 0.5 mm, respectively. Also, airbag
deployment performance tests were performed on airbag covers prepared
from specimens 1 to 3 at a low temperature (-35 degrees centigrade), a
room temperature, and a high temperature (85 degrees centigrade). These
evaluations show that an airbag cover as specimen 1 does not pose any
problem at the room temperature and the high temperature, but produces
the problem that its hinge fractures and its door breaks away at the low
temperature. Also, an airbag cover as specimen 2 does not pose any
problem at all these temperatures with no breaking away of the door.
Furthermore, an airbag cover as specimen 3 does not have the problem of
breaking away of the door at the high temperature, but experiences the
problem of partial fracture of the hinge portion, and experiences the
problem of fracture of the hinge and breaking away of the door at the low
temperature and the room temperature.

[0042]The above-described results of the property evaluation and the
product evaluation reveal that specimen 2 is suitable to the airbag cover
according to the present invention. In addition, comparison of the
results of the property evaluation performed on specimens 1 to 3 finds
that tensile break strength of 15 MPa or more is preferable, and
experience shows that 40 MPa is more preferable. Furthermore, stretch at
break of 600% or more is preferable. However, according to the property
evaluation in FIG. 3, "600% or more" means that 100% or 200% is not
included and that stretch at break of about 500% may lead to product
commercialization if the tensile break strength is adjusted. Also, it is
preferable that a specimen having a notch formed does not break (N.B.)
away when subjected to Izod impact strength tests at -35 degrees
centigrade or more. In other words, it is preferable that the material
constituting the airbag cover 1 (plate-like portion 11 and inner case 12)
according to the present invention is an olefin thermoplastic resin (TPO
material) which meets: (A) bending modulus of elasticity (JIS-K7203): 500
to 1000 MPa, (B) tensile break strength: 15 to 40 MPa, (C) stretch at
break: 600% or more, (D) Izod impact strength: not to break away at -35
degrees centigrade or more.

[0043]Described below is the fact that an airbag cover employing an olefin
thermoplastic resin (TPO material) of the above-mentioned specimen 2 is
suitable for a medium-size airbag cover. FIGS. 4(A) and 4(B) show the
relationship between material for use in airbag cover and the surface
area. FIG. 4(A) shows the relationship between airbag cover surface area
and deflection. FIG. 4(B) shows the relationship between airbag cover
surface area and weight.

[0044]In FIG. 4(A), F1 indicates the test results for a TPO material used
in a small, conventional airbag cover, F1 indicates those for a PP
material used in a large, conventional airbag cover, and F3 indicates
those for a TPO material of the afore-mentioned specimen 2. Airbag covers
having surface area of 500 cm2, 1500 cm2, and 2500 cm2
respectively, are prepared, and deflection is measured when they are
subjected to a load equal to an impact created at the time of airbag
inflation and deployment. As a result, an airbag cover having surface
area of 500 cm2 exhibits a deflection of 2 mm for F1, 1 mm for F2,
and 1.5 mm for F3. Also, an airbag cover having surface area of 1000
cm2 exhibits a deflection of 4 mm for F1, 1 mm for F2, and 2 mm for
F3. Furthermore, an airbag cover having surface area of 2500 cm2
exhibits a deflection of 8 mm for F1, 1.5 mm for F2, and 3 mm for F3. For
this test, the allowable limit for deflection is empirically 3 mm.
Accordingly, an airbag cover whose deflection falls within the shaded
region in FIG. 4(A) is not suitable for product commercialization. As for
a medium-size airbag cover having surface area of 1000 to 2000 cm2,
the TPO material (F1) used in the small, conventional airbag cover is not
suitable for the medium-size airbag cover since its deflection exceeds 3
mm.

[0045]In FIG. 4(B), G2 indicates the test results for a TPO material used
in a small-sized, conventional airbag cover, G2 indicates those for a PP
material used in a large, conventional airbag cover, and G3 indicates
those for a TPO material of the afore-mentioned specimen 2. Airbag covers
having surface area of 500 cm2, 1500 cm2, and 2500 cm2,
respectively, are prepared and weighed. As a result, an airbag cover
having surface area of 500 cm2 weighs about 310 grams for G1, about
580 grams for G2, and about 290 grams for G3. Also, an airbag cover
having surface area of 1000 cm2 weighs about 580 grams for G1, about
800 grams for G2, and about 570 grams for G3. Furthermore, an airbag
cover having surface area of 2500 cm2 weighs about 970 grams for G1,
about 1100 grams for G2, and about 780 grams for G3. For this test, the
allowable limit of weight is empirically about 1000 grams, but is set at
800 grams since reduced weight is preferable. Accordingly, an airbag
cover whose weight falls within the shaded region in FIG. 4(B) is not
suitable for product commercialization. As for a medium-size airbag cover
having surface area of 1000 to 2000 cm2, the PP material (G2) used
in the large, conventional airbag cover is not suitable for the
medium-size airbag cover since its weight exceeds 800 grams.

[0046]As described above, the TPO material of specimen 2 is suitable for a
medium-size airbag cover having surface area of 1000 to 2000 cm2 in
terms of deformation and weight. On the contrary, the TPO and PP material
that are used in conventional airbag covers are not suitable for the
medium-sized airbag cover unless modified.

[0047]The specific shape of the airbag cover according to the present
invention is described below. FIGS. 5(A)-5(C) are views showing an airbag
cover according to the present invention. FIG. 5(A) is a cross-sectional
view. FIG. 5(B) is an enlarged view of a section indicated by "B" in FIG.
5(A). FIG. 5(C) is an enlarged view of a section indicated by "C" in FIG.
5(A). FIGS. 6(A) and 6(B) are views showing an airbag cover according to
the present invention. FIG. 6(A) is a rear view. FIG. 6(B) is a
cross-sectional view taken along the line B-B of FIG. 6(A). The
cross-sectional view in FIG. 5(A) is a cross-sectional view taken along
the line A-A of FIG. 6(A).

[0048]The airbag cover as shown in FIGS. 5(A)-5(C) and 6(A)-6(B) is an
airbag cover formed by integrally molding a plate-like portion 11
constituting a vehicle interior surface and an inner case 12 that is
disposed on the back face of the plate-like portion 11 and constitutes an
airbag inflation and deployment path. The plate-like portion 11 include a
door 11 a formed so as to split open when the airbag inflates and
deploys, and a hinge 15 that rotatably supports the door 11a. The hinge
15 includes a thinner portion 15a formed in a connecting section between
the an inner case 12 and the plate-like portion 11 and a plurality of
ribs 15b disposed on the outer surface of the thinner portion 15a so as
to be bendable and bucklable when the airbag inflates and deploys.

[0049]The plate-like portion 11 is a component that constitutes part of a
vehicle interior surface of an instrument panel 2 and is constructed to
have surface area of 1000 to 2000 cm2. Also, the plate-like portion
11 has a wall thickness of 2.5 to 3.5 mm which is smaller than
conventional ones. As shown in FIG. 6(A), the plate-like portion 11 has
an inner case 12 installed upright on a rear face thereof. The inner case
12 is disposed at least 30 mm away from a rim 11e of the plate-like
portion 11. The plate-like portion 11 has a substantially H-shaped tear
line 11b formed at its portion corresponding to the inner case 12, the
tear line 11b being thinner (wall thickness: dt) than the plate-like
portion 11. When the airbag inflates, the tear line 11b allows the
plate-like portion 11 to split open therealong and turn like double
doors, thereby allowing the airbag to be released into the passenger
compartment for inflation and deployment. The portions that split open
along the tear line 11b constitute doors 11a. The opening formed by
opening doors 11a generally has an area of 250 to 300 cm2.
Accordingly, the plate-like portion 11 has a surface area approximately 3
to 8 times that of the opening.

[0050]As shown in FIG. 6(A), the plate-like portion 11 has at least one
first reinforcement rib 11c disposed in a reticular pattern on a back
face thereof for reinforcement. The first reinforcement rib 11c is
disposed in an appropriate manner, depending on the size and shape of the
plate-like portion 11, and its shape is not limited to the shape as shown
in FIG. 6(A). The first reinforcement rib 11c has a height of, for
example, 2 to 5 mm, while it has a pitch of, for example, 15 to 30 mm.
Also, the thickness d1 of the first reinforcement rib 11c may be
substantially equal to that of a rib 15 to be mentioned later.
Preferably, the thickness d1 of the first reinforcement rib 11c is 1.0 to
1.3 mm. The first reinforcement rib 11c formed to have smaller thickness
than a conventional reinforcement rib (1.3 to 1.8 mm thick) suppresses
the occurrence of a sink, thereby enhancing the appearance of the airbag
cover 1. If the thickness d1 larger than 1.3 mm does not cause the
occurrence of a sink due to the relationship with the height of the first
reinforcement rib 11c, the same thickness as conventional reinforcement
ribs may be adopted.

[0051]As shown in FIG. 6(A), a plurality of second reinforcement ribs 11d
for reinforcing the inner case 12 are disposed at a leg portion 12a of
the inner case 12 disposed along the tear line 11b. As shown in FIG.
6(B), the second reinforcement rib 11d has a substantially triangle shape
so as to be connected to the back face of the plate-like portion 11 and
the leg portion 12a. Like the first reinforcement rib 11c, the second
reinforcement rib 11d is a rib for reinforcement, and therefore its
thickness d2 is the same as the thickness d1 of the first reinforcement
rib 11c. However, since the second reinforcement rib 11d is often formed
to have a larger height than the first reinforcement rib 11c, preferably
the second reinforcement rib 11d has substantially the same thickness
(for example, 1.0 to 1.3 mm) as the rib 15b.

[0052]As shown in FIGS. 5(A) and 6(A), the plate-like portion 11 has a rim
11e formed at its outer circumferential edge and a clip 11f installed
upright on its back face for locating itself, and is mounted to the
instrument panel 2 by connecting the clip 11f to a locking hole formed in
the instrument panel 2 and setting the rim 11e into an opening in the
instrument panel 2.

[0053]As shown in FIGS. 5(A) and 6(A), the inner case 12 is constructed
with the tubular leg 12 installed upright in a rectangular shape on the
back face of the plate-like portion 11. Since the plate-like portion 11
is mounted to the instrument panel 2 in such a manner that its top
surface faces occupants and the airbag is inflated and deployed toward
these occupants, the inner case 12 is often slanted in relation to the
plate-like portion I1. The airbag cover 1 according to the present
invention is formed by resin-molding of the inner case 12 and the
plate-like portion 11 in an integral manner. Such an integral airbag
cover 1 experience a great change in thickness of a resin layer at a
connecting section between the plate-like portion 11 and the leg portion
12a of the inner case 12, which causes a significant contraction when a
resin sets and a concave or so called a sink on the plate-like portion 11
along the leg portion 12a, degrading the appearance of the airbag cover
1. In order to suppress the occurrence of the sink or minimize the sink
to such a degree that it is invisible to the human eye, a connection
section between the plate-like portion 11 and the leg portion 12a of the
inner case 12 must be thinned as much as possible. Accordingly, the
airbag cover as shown in the figure has the connection section between
the plate-like portion 11 and the leg portion 12a of the inner case 12
formed to be as thinner as possible, whereby a bendable portion (that is,
a thinner portion 15a) is utilized as a hinge portion 15.

[0054]The hinge portion 15 is a portion which allows the door 11a to turn
toward the top surface of the plate-like portion 11 to form a release
section along the inner case 12, through which the airbag is smoothly
released into the passenger compartment. Since the function of the hinge
portion 15 affects how the airbag deploys, the hinge portion 15 must
allow the door 11a to turn as soon as the airbag inflates and deploys. In
addition, the hinge portion 15 must anchor the door 11a firmly to the
plate-like portion 11 to ensure that the door 11a does not break away. In
other words, the hinge portion 15 must be bendable and resistant to
deformation.

[0055]As shown in FIG. 5(B), the hinge portion 15 indicated by "B" in FIG.
5(A) connects the plate-like portion 11 with the leg portion 12a of the
inner case 12 and has a thinner portion 15a formed to have a smaller
thickness than the leg portion 12a or the plate-like portion 11 and a rib
15b disposed on the outside of the thinner portion 15a. The thickness d
of the thinner portion 15a is substantially equal to or less than the
thickness dt of the tear line 11b. Specifically, the thickness d of the
thinner portion 15a is preferably 0.5 to 1.5 mm. The thinner portion 15a
formed to be thin to such a degree suppresses the occurrence of a sink
and minimizes the sink to such a degree that it is invisible to the human
eye, thereby enhancing the appearance of the airbag cover 1. Also, the
thinner portion 15a is formed on the outside of the inner case 12 so as
to be slanted to allow the door 11a to easily turn. The height of the
thinner portion 15a is set at, for example, 3 to 5 mm.

[0056]As shown in FIG. 5(B), the rib 15b is formed in a trapezoidal shape
so as to connect the back face of the plate-like portion 11, the thinner
portion 15a, and leg portion 12a. The rib 15b must be a component for
reinforcing the thinner portion 15a as well as a bendable and bucklable
component which allows the door 11a to smoothly turn. In addition, the
thickness dr of the rib 15b must be reduced to such a degree that a sink
does not occur on the surface of the plate-like portion 11 since the rib
15b is connected to the back face of the plate-like portion 11.
Consequently, the thickness dr of the rib 15b is larger than the
thickness d of the thinner portion 15a and smaller than the thickness of
conventional reinforcement ribs. Specifically, the thickness dr of the
rib 15b is preferably 1.0 to 1.3 mm. The strength of the rib 15b can be
adjusted by the number of the ribs and the ribs are continuously disposed
at a pitch of 3 to 15 mm. In particular, disposition at a pitch of 4 to
10 mm is effective. The disposition of the rib 15b on the outside of the
thinner portion 15a reinforces the thinner portion 15 as well as
effectively absorbs an impact generated at the time of turning door by
bending and buckling. If the strength of the rib 15b can be sufficiently
adjusted by the number (pitch) of ribs, the thickness dr of the rib 15b
may be substantially equal to the thickness d of the thinner portion 15a.

[0057]As shown in FIG. 5(C), the thinner portion 15a may be formed in an
extension 12b extending from the inner case 12. As shown in FIG. 6(A),
the extension 12b extends outward over the entire hinge portion 15. As
described above, the extension 12b formed in the leg portion 12a of the
inner case 12 allows the pivot of the door 11a to be shifted outward by a
distance r from the inner face of the inner case 12, thereby enabling the
door 11a to more easily turn. As shown in FIG. 5(C), the rib 15b may be
formed in a substantially triangle shape so as to connect the back face
of the plate-like portion 11, the thinner portion 15a, and leg portion
12a.

[0058]A connecting section between the plate-like portion 11 and the inner
case 12 is also present at a portion which does not constitute the hinge
portion 15, namely, the leg portion 12a disposed along the tear line 11b
and reinforced by the second reinforcement rib 11d. As shown in FIG.
6(B), a thinner portion 12c that is provided under substantially the same
conditions as the thinner portion 15a may be formed at this connection
section. The thinner portion 12c does not constitute the hinge portion
15, and therefore needs not consider ease of turning of the door 11a and
may be formed so as to extend straight toward the plate-like portion 11
from the leg portion 12a. Although the thinner portion 12c is formed
along the inner surface of the inner case 12 in FIG. 6(B), it may be
formed on the external surface of the inner case 12 or in the middle of
the leg portion 12a.

[0059]FIGS. 7(A) and 7(B) are schematic illustrations showing part of
manufacturing process of an airbag cover according to the present
invention. FIG. 7(A) shows a molding process of a thinner portion. FIG.
7(B) shows a working process of a tear line. The rib 15b, the first
reinforcement rib 11c, and the second reinforcement rib 11d are omitted
in these figures. When the afore-mentioned thinner portions 15a, 12c are
formed in a connecting section between the plate-like portion 11 and the
inner case 12, molds 71, 72, for example, as shown in FIG. 7(A) may be
used. When the thinner portion 15a is formed, a pair of molds 71, 72 are
disposed inside the inner case 12 for resin molding. After a resin sets,
each of the molds 71 is moved in the direction by an arrow in the figure
and removed from the resin molding. When the thinner portion 12c is
formed, a pair of molds 71, 72 are disposed on the outside of the inner
case 12 for resin molding. After a resin sets, each of the molds 72 is
moved in the direction by an arrow in the figure and removed from the
resin molding.

[0060]As shown in FIG. 7(B), the tear line 11b is formed in a substantial
H shape by machining, laser beam machining, or ultrasonic machining after
molding of the airbag cover 1. This simplifies the mold of the airbag
cover 1, reducing the cost of mold design and manufacturing.

[0061]The effect of the airbag cover 1 is described below. FIGS. 8(A) and
8(B) are illustrations showing how an airbag inflates and deploys. FIG.
8(A) shows an airbag just before released to the passenger compartment.
FIG. 8(B) shows an airbag immediately after released to the passenger
compartment. The reference numerals and symbols in FIG. 8 refer to the
same components as those of the airbag cover 1 with the same reference
numerals and symbols in FIGS. 5 and 6, and repeated description are
omitted.

[0062]As shown in FIG. 8(A), when receiving gas supply from an inflator
(not illustrated) in the event of an emergency such as a crash, an airbag
81 begins to inflate in an inner case 12 and comes into contact with
doors 11a of a plate-like portion 11. Then, due to the pressure exerted
by the inflating airbag the doors 11a split open along a tear line 11b
formed to have a smaller wall thickness. Like double-doors, the doors 11a
turn upward and downward, respectively, about a hinge portion 15 as a
supporting point, as shown in FIG. 8(B). Since the hinge 15 has a thinner
portion 15a formed to have a smaller wall thickness, the plate-like
portion 11 deforms around the thinner portion 15a, functioning as the
hinge portion 15 for the doors 11a.

[0063]As described above, the thinner portion 15a has a thickness d equal
to or less than that of the tear line 11b. However, a reinforcement
formed by a rib 15b having a larger thickness dr than the tear line 11b
and the thinner portion 15a prevents the thinner portion 15a from
fracturing when the thinner portion 15a is subjected to stress created by
turning doors 15a. To effectively prevent the thinner portion 15a from
fracturing, the thickness dr, the number of the ribs (pitch), or the
volume can be adjusted such that the thinner portion 15a withstands the
stress created at the hinge portion 15 when the airbag 81 inflates and
deploys.

[0064]As shown in FIG. 8(B), when each of the doors 11a turns about the
hinge portion 15 as a supporting point, the hinge portion 15 and the
plate-like portion 11 in the vicinity deform in conjunction with turning
doors, causing the rib 15b to be compressed by the plate-like portion 11,
the thinner portion 15a, and the leg portion 12a (including the extension
12b). As the hinge portion 15 deforms, the rib 15b gradually bends and
finally buckles. The bending and buckling rib 15b effectively absorbs
impact created by centrifugal force involved in turning doors 11a,
thereby allowing the doors 11a to smoothly turn and preventing the doors
11a from breaking away. An extension 12b formed at the leg portion 12a of
the inner case 12 allows the supporting point of the doors 11a to be
shifted outward, which causes the doors 11a to more easily turn. As shown
in FIG. 8(B), this enables the door 11a connected to the hinge 15 having
the extension 12b to turn earlier than the other door 11a. Such a time
difference involved in the turning of the doors 11a provides directional
characteristics to the inflation and deployment of the airbag 81, thereby
allowing the airbag 81 to be effectively inflated and deployed in the
desired direction (toward the occupants).

[0065]An airbag apparatus according to the present invention is described
below. FIG. 9 is a cross-sectional view of an airbag according to the
present invention. The reference numerals and symbols in FIG. 9 refer to
the same components as those of the airbag cover 1 with the same
reference numerals and symbols in FIGS. 5 and 6, and repeated description
are omitted.

[0066]An airbag apparatus as shown in FIG. 9 includes an airbag (not
illustrated) that is normally stored in a folded state and inflates and
deploys in the event of an emergency, an inflator 91 for supplying gas to
the airbag, a retainer 92 that at least stores the airbag and has a hook
92 provided on an external surface thereof, and an airbag cover 1 which
locks the retainer 92 thereto and constitutes a vehicle interior surface,
wherein the airbag cover 1 is formed by integrally molding a plate-like
portion 11 constituting part of an instrument panel 2 disposed in front
of an occupant and an inner case 12 disposed on the back face of the
plate-like portion 11, which constitutes an airbag inflation and
deployment path and has a locking hole 12d at its leg portion 12a to
which the hook 92a is locked. The above-described airbag 1 cover
according to the present invention is used for the airbag cover 1. The
inflator 91 may be mounted on the outside of the retainer 92 instead of
being housed inside the retainer 92. The retainer 92 is connected to a
fixing component 94 via a connecting component 93.

[0067]The airbag apparatus is a passenger airbag that is installed on the
instrument panel 2 disposed in front of a passenger seat P (see FIG.
1(A)). Accordingly, the top surface of the airbag cover 1 constitutes
part of the instrument panel 2. In addition, the above-described airbag
cover 1 according to the present invention is used for the airbag cover
1. This results in a reduction in the number of components and a
reduction of man-hours as well as ensures the rigidity of the instrument
panel 2 despite the use of a soft resin. Furthermore, this allows a seam
between the airbag cover 1 and the instrument panel 2 to be disposed so
as to be hardly visible to or hidden from occupants in the driver's sear
D and the passenger seat P, thereby keeping aesthetically pleasing
appearance.

[0068]The thinner portion 15a formed in a connecting section between the
plate-like portion 11 and the inner case 12 suppresses deformation of the
connecting section resulting from contraction associated with curing of a
resin, which prevents sink from occurring on the surface of the airbag
cover 1, resulting in improvement in the appearance of the airbag cover
1. In addition, a plurality of ribs 15b disposed on the outer surface of
the thinner portion 15a of the hinge 15 eliminates the necessity for a
thinner portion constituting a hinge 15 to be separately formed in the
plate-like portion 11, resulting in a simplified structure of the hinge
15. Furthermore, the ribs 15b formed so as to be bendable and bucklable
can absorb an impact created at the time of turning of the door 11a,
thereby effectively preventing the door 11a from breaking away.

[0069]As described in FIG. 4(B), the TPO material used in the airbag cover
according to the present invention has an advantage of light weight.
Accordingly, in the leg portion 12a of the inner case 12, a portion where
a locking hole 12d is formed can have a larger wall thickness than the
plate-like portion 11 or a conventional leg portion, thereby enhancing
rigidity. Consequently, an airbag apparatus that is more resistant to
impact associated with airbag deployment than conventional airbag
apparatuses can be provided. Conventional airbag apparatuses need 10 to
14 locking holes 12d, while the airbag apparatus according to the present
invention results in reduction to 8 to 10 locking holes 12d as well as
reduction in the number of the metal hooks 92a, leading to cost reduction
and weight reduction.

[0070]The present invention is not limited to the above embodiment, and
can be applied to an airbag cover and an airbag apparatus that have a
tear line 11b formed in a U-shape with a single door. Needless to say, a
reinforcement rib may be disposed on the inside of the thinner portion
15a. Various modifications are conceivable within the scope of the
present invention.